title: Characterization of the role of EGF-A of low density lipoprotein receptor in PCSK9 binding.
abstract: Proprotein convertase subtilisin kexin-like 9 (PCSK9) promotes the degradation of low density lipoprotein receptor (LDLR) and plays an important role in regulating plasma LDL-cholesterol levels. We have shown that the epidermal growth factor precursor homology domain A (EGF-A) of the LDLR is critical for PCSK9 binding at the cell surface (pH 7.4). Here, we further characterized the role of EGF-A in binding of PCSK9 to the LDLR. We found that PCSK9 efficiently bound to the LDLR but not to other LDLR family members. Replacement of EGF-A in the very low density lipoprotein receptor (VLDLR) with EGF-A of the LDLR promoted the degradation of the mutant VLDLR induced by PCSK9. Furthermore, we found that PCSK9 bound to recombinant EGF-A in a pH-dependent manner with stronger binding at pH 6.0. We also identified amino acid residues in EGF-A of the LDLR important for PCSK9 binding. Mutations G293H, D299V, L318D, and L318H reduced PCSK9 binding to the LDLR at neutral pH without effect at pH 6.0, while mutations R329P and E332G reduced PCSK9 binding at both pH values. Thus, our findings reveal that EGF-A of the LDLR is critical for PCSK9 binding at the cell surface (neutral pH) and at the acidic endosomal environment (pH 6.0), but different determinants contribute to efficient PCSK9 binding in different pH environments.
authors.affiliation: Departments of Pediatrics and Biochemistry, Group on the Molecular and Cell Biology of Lipids, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
authors.forename: Hong-mei
authors.initials: HM
authors.lastname: Gu
authors.forename: Ayinuer
authors.initials: A
authors.lastname: Adijiang
authors.forename: Matthew
authors.initials: M
authors.lastname: Mah
authors.forename: Da-wei
authors.initials: DW
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D017124:Conserved Sequence; D004815:Epidermal Growth Factor / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009154:Mutation; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000378:metabolism*; D011485:Protein Binding; D011498:Protein Precursors / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D011973:Receptors, LDL / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism*
chemical_list: C573412:LDLR protein, human; D011498:Protein Precursors; D011973:Receptors, LDL; C042652:epidermal growth factor precursor; D004815:Epidermal Growth Factor; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases
keywords: epidermal growth factor precursor homology domain A; ligand binding; proprotein convertase subtilisin kexin-like 9